Reference is hereby made to the following, commonly assigned, co-pending, U.S. Patent Applications which disclose common subject matter:
Ser. No.09/290,967 filed on Apr. 13, 1999 for DUAL-CHAMBER PACEMAKER WITH OPTIMIZED PVARP FOLLOWING A PVC filed in the names of R. Betzold et al.; Ser. No. 09/067,729 filed Apr. 28, 1998 for MULTIPLE CHANNEL, SEQUENTIAL, CARDIAC PACING SYSTEMS filed in the names of C. Struble et al.; Ser. No. 09/439,569 filed on even date herewith for CARDIAC PACING SYSTEM DELIVERING MULTI-SITE PACING IN A PREDETERMINED SEQUENCE TRIGGERED BY A SENSE EVENT in the names of C. Yerich et al.; Ser. No. 09/439,565 filed on even date herewith for BI-CHAMBER CARDIAC PACING SYSTEM EMPLOYING UNIPOLAR LEFT HEART CHAMBER LEAD IN COMBINATION WITH BIPOLAR RIGHT HEART CHAMBER LEAD in the names of B. Blow et al.; Ser. No. 09/439,078 filed on even date herewith for MULTI-SITE CARDIAC PACING SYSTEM HAVING TRIGGER PACE WINDOW in the names of C. Juran et al.; Ser. No. 09/439,568 filed on even date herewith for RECHARGE CIRCUITRY FOR MULTI-SITE STIMULATION OF BODY TISSUE filed in the names of B. Blow et al.; and Ser. No. 09/439,243 filed on even date herewith for AV SYNCHRONOUS CARDIAC PACING SYSTEM DELIVERING MULTI-SITE VENTRICULAR PACING TRIGGERED BY A VENTRICULAR SENSE EVENT DURING THE AV DELAY in the names of C. Yerich et al.
The present invention pertains to multi-site cardiac pacing systems for pacing first and second sites of a patient""s heart, particularly right and left heart chambers, e.g., the right and left ventricles, and operable in selected pacing modes while avoiding inappropriate responses to double sensing of an evoked depolarization conducted between the sites.
In diseased hearts having conduction defects and in congestive heart failure (CHF), cardiac depolarizations that naturally occur in one upper or lower heart chamber are not conducted in a timely fashion either within the heart chamber or to the other upper or lower heart chamber. In such cases, the right and left heart chambers do not contract in optimum synchrony with each other, and cardiac output suffers due to the conduction defects. In addition, spontaneous depolarizations of the left atrium or left ventricle occur at ectopic foci in these left heart chambers, and the natural activation sequence is grossly disturbed. In such cases, cardiac output deteriorates because the contractions of the right and left heart chambers are not synchronized sufficiently to eject blood therefrom. Furthermore, significant conduction disturbances between the right and left atria can result in left atrial flutter or fibrillation.
It has been proposed that various conduction disturbances involving both bradycardia and tachycardia of a heart chamber could benefit from pacing pulses applied at multiple electrode sites positioned in or about a single heart chamber or in the right and left heart chambers in synchrony with a depolarization which has been sensed at at least one of the electrode sites. It is believed that cardiac output can be significantly improved when left and right chamber synchrony is restored, particularly in patients suffering from dilated cardiomyopathy and CHF.
A number of proposals have been advanced for providing pacing therapies to alleviate these conditions and restore synchronous depolarization and contraction of a single heart chamber or right and left, upper and lower, heart chambers as described in detail in commonly assigned U.S. Pat. Nos. 5,403,356, 5,797,970 and 5,902,324 and in U.S. Pat. Nos. 5,720,768 and 5,792,203 all incorporated herein by reference. The proposals appearing in U.S. Pat. Nos. 3,937,226, 4,088,140, 4,548,203, 4,458,677, 4,332,259 are summarized in U.S. Pat. Nos. 4,928,688 and 5,674,259, all incorporated herein by reference. The advantages of providing sensing at pace/sense electrodes located in both the right and left heart chambers is addressed in the ""688 and ""259 patents, as well as in U.S. Pat. Nos. 4,354,497, 5,174,289, 5,267,560, 5,514,161, and 5,584,867, also all incorporated herein by reference.
The medical literature also discloses a number of approaches of providing bi-atrial and/or bi-ventricular pacing as set forth in: Daubert et al., xe2x80x9cPermanent Dual Atrium Pacing in Major Intra-atrial Conduction Blocks: A Four Years Experiencexe2x80x9d, PACE (Vol. 16, Part II, NASPE Abstract 141, p.885, April 1993); Daubert et al., xe2x80x9cPermanent Left Ventricular Pacing With Transvenous Leads Inserted Into The Coronary Veinsxe2x80x9d, PACE (Vol. 21, Part II, pp. 239-245, Jan. 1998); Cazeau et al., xe2x80x9cFour Chamber Pacing in Dilated Cardiomyopathyxe2x80x9d, PACE (Vol. 17, Part II, pp. 1974-1979, November 1994); and Daubert et al., xe2x80x9cRenewal of Permanent Left Atrial Pacing via the Coronary Sinusxe2x80x9d, PACE (Vol. 15, Part II, NASPE Abstract 255, p. 572, April 1992), all incorporated herein by reference.
Problems surface in implementing multi-site pacing in a single heart chamber or in right and left heart chamber pacing within the contexts of conventional timing and control systems for characterizing and responding to sense event signals generated by sense amplifiers coupled to spaced apart pace/sense electrodes. Inappropriate responses can be triggered by depolarizations conducted between the separated pace/sense electrode sites and sensed by sense amplifiers coupled to those pace/sense electrodes which upset the timing of delivery of subsequent pacing pulses. In right and left heart pacing systems, pacing and sensing problems arise when right-to-left or left-to-right conduction delays vary depending on right and left ventricle pace/sense electrode placement, transient conditions of the heart, and chronic CHF.
In modern cardiac pacemakers, it is common to define certain blanking and refractory periods commenced after delivery of a pacing pulse and sensing of a depolarization wave traversing the pace/sense electrode. The input terminals of the sense amplifier are effectively uncoupled from the pace/sense electrodes during the blanking periods following delivery of a pacing pulse. The blanking periods are shorter than refractory periods which are started after both sense events and delivery of pacing pulses.
Sense events detected by a sense amplifier following time-out of a blanking period and during timing out of its refractory periods are characterized as xe2x80x9crefractory sense eventsxe2x80x9d, and sense events occurring after time-out of the refractory periods are characterized as xe2x80x9cnon-refractory sense eventsxe2x80x9d. Non-refractory sense events trigger restarting pacing escape intervals or the AV delay in AV synchronous pacemakers. Refractory sense events restart various post-event time periods including refractory periods as described further below to avoid inappropriate tracking of repetitive noise signals that are mistakenly detected as sense events.
A delivered pacing pulse xe2x80x9ccapturesxe2x80x9d the heart if its delivery to a pace/sense electrode causes or xe2x80x9cevokesxe2x80x9d a myocardial contraction and depolarization wave that is conducted away from that pace/sense electrode site. The depolarization wave and accompanying contraction can be delayed in diseased hearts such that the depolarization wave can be sensed by a sense amplifier coupled to another pace/sense electrode at another site spaced from the paced pace/sense electrode site. The evoked depolarization wave can reach the non-paced pace/sense electrodes after time-out of the post-pace blanking period of the sense amplifier and be sensed during a post-event time period, e.g., a refractory period and be mistakenly characterized as a refractory sense event. The delayed sensing in one or the other of the paced sites can also occur if the pacing pulse delivered at that site fails to capture the heart. The mistakenly characterized refractory sense event restarts post-event blanking and refractory periods. The restarting of these post-event time periods can interfere with the sensing or proper characterization of subsequent true spontaneous depolarizations and disrupt delivery of pacing pulses.
In bi-chamber (bi-atrial or bi-ventricular) pacemakers, pacing pulses are delivered to one or the other or both of the right and left heart chambers upon expiration of a pacing escape interval. The escape interval is restarted upon delivery of a pacing pulse or upon a non-refractory sense event. Post-event time periods are started upon delivery of a pacing pulse or upon a refractory or non-refractory sense event. The delayed right-to-left or left-to-right conduction of an evoked depolarization resulting from delivery of a pacing pulse to the right or left heart chamber, respectively, and capture of that heart chamber traverses the non-paced pace/sense electrode after a delay that enables it to be sensed and mistakenly characterized as a refractory sense event Similarly, the delayed right-to-left or left-to-right conduction of a spontaneous depolarization occurring first in the right or left heart chamber, respectively, traverses the second pace/sense electrode after a delay that enables it to be sensed again and mistakenly characterized the second time as a refractory sense. Here also, a second restarting of post-event time periods due to a mistakenly characterized refractory sense event can result in the failure to respond appropriately to the next true, spontaneous sense event in either of the right and left heart chambers. Thus, the timing of delivery of bi-atrial or bi-ventricular pacing pulses can also be disrupted.
Similar problems arise in AV sequential, bi-atrial and/or bi-ventricular pacing systems of the types described above. A V-A pacing escape interval is typically restarted by one of the following events: delivery of a ventricular pacing pulse at the time-out of an AV delay; a spontaneous, non-refractory, ventricular sense event sensed in one ventricle before the time-out of the AV delay; or a spontaneous, non-refractory, ventricular sense event sensed in one ventricle before the time-out of the V-A escape interval. A set of post-ventricular event timers are started upon each such event and time out post-ventricular event periods, e.g. atrial and ventricular blanking periods and refractory periods and the URI. The post-ventricular event timers start at least one post-ventricular event period that affects the treatment of an atrial sense event occurring during its time-out. For example, an atrial sense event occurring during the time-out of a post-ventricular atrial refractory period (PVARP) can be ignored for purposes of resetting the V-A escape interval and starting the AV delay. The PVARP is typically programmable and can be set to prevent any response to an atrial sense event that may be caused by sensing of the antegrade conduction of the spontaneous or evoked ventricular depolarization through the atria and to the atrial pace/sense electrodes.
The PVARP, VRP (Ventricular Refractory Period) and URI interval are restarted each time that a ventricular pacing pulse is delivered and whenever a refractory or non-refractory ventricular sense event occurs. It is important to note that the hearts of patients in CHF frequently exhibit wide QRS complexes and prolonged conduction delays of up to 200 msec between electrodes implanted in relation to the right and left ventricles. This prolonged delay results in the possibility of sensing right and left ventricular sense events caused by the same spontaneous ventricular depolarization at times that are so separated that the second ventricular sense event restarts the post-event time periods, particularly the PVARP, that were started upon the earlier ventricular sense event of the same depolarization. The restarting of the PVARP can cause a true atrial sense event to be mistakenly characterized as a refractory atrial sense event which cannot terminate the V-A escape interval and restart the AV delay. This can cause loss of atrial and ventricular synchronization and effectively reduces the atrial rate that can be tracked. The restarting of the URI can lead to the extension of the AV delay, and the restarting of the VRP can cause a true ventricular depolarization to be characterized as a refractory ventricular sense event.
Similar timing problems may occur if triggered pacing pulses are delivered at multiple sites in a single heart chamber, and other timing issues occur with restarting of pacing escape intervals in any of the above described situations. These problems and how we address them are described within.
The present invention is therefore directed to providing multi-site pacing in a single heart chamber or right and left heart chamber pacing methods and systems that avoid prolonging post-event timing periods that cause pacing to be inhibited or to revert to asynchronous pacing because of a delayed conduction of a single depolarization between sense sites in the same or the right and left heart chambers.
In accordance with the invention, the delivery of a pacing pulse at the time-out of a preceding pacing escape interval or a non-refractory right or left chamber sense event during the pacing escape interval restarts the pacing escape interval, typical post-pace or post-sense time periods, and a conditional refractory period. The conditional refractory period is set to embrace the delayed conduction time of an abnormally conducted depolarization between spaced apart sense sites in the same or the right and left heart chambers.
A sense event that occurs during the conditional refractory period is treated as a refractory sense event and extends, e.g., by restarting, the post-sense periods except for the conditional refractory period. But, the restarted post-sense time periods are adjusted in relation to the time of occurrence of the refractory sense event within the conditional refractory period. The restarted post-sense time periods are preferably shortened by the elapsed time of the conditional refractory period. The shortened post-sense periods enable appropriate response to noise if further sense events occur during time-out of the restarted post-sense periods but are not so prolonged as to prevent legitimate sense events from restarting the pacing escape interval.
The present invention is preferably implemented in pacing systems for pacing and sensing at spaced apart pace/sense electrode sites in a single heart chamber or pacing and sensing at pace/sense electrode sites in right and left heart chambers to provide bi-atrial and/or bi-ventricular pacing.
The present invention has a number of advantages flowing from negating the extension of the post-event time periods in response to a sense event occurring within the conditional refractory period. A principal advantage is that a subsequent true sense event occurring after the time-out of the post-event time periods will not be characterized as a refractory sense event as it would have been if the post-event time periods were restarted for their full length. However, the post-event time periods are restarted for their full lengths if a second sense event occurs during their time-out, on the assumption that the closely timed first and second refractory sense events represent noise.
Other advantages include the ability to accumulate data related to the occurrences of refractory sense events during the conditional refractory period and closely following its time-out for diagnostic purposes. The occurrences of refractory sense events and their timing within the conditional refractory period and outside the conditional refractory period can be retained in in Implantable Pulse Generator (IPG) memory for retrieval and analysis at a later time or may be used by on-board algorithms to adjust pacing and sensing parameters. For example, the data may be useful in determining that loss of capture has occurred when a pacing pulse is followed by a refractory sense event within the conditional refractory period. The pacing pulse energy can be increased either automatically or by a physician upon reviewing the retrieved data. Or, the conditional refractory period may be automatically extended or extended by the physician upon reviewing the data if refractory sense events following a non-refractory sense event tend to first occur just after the end of the conditional refractory period.
The present invention is preferably implemented into an external or implantable pulse generator and lead system selectively employing right and left heart, atrial and/or ventricular leads. The preferred embodiment is implemented in an architecture that allows wide programming flexibility for operating in AV synchronous modes with right and left ventricular pacing or in atrial or ventricular only modes for providing only right and left atrial or ventricular pacing. The AV synchronous embodiments may be implemented into an IPG or external pulse generator and lead system providing right and left ventricular pacing and sensing and either both right and left atrial pacing or just right or left atrial pacing and sensing. Alternatively, the invention can be implemented in IPGs or external pulse generators and lead systems having hard wired connections and operating modes that are not as programmable.